The tumor microenvironment, composed of non-cancer cells and their stroma, has become recognized as a major factor influencing the growth of cancer. The microenvironment has been implicated in the regulation of cell growth, determining metastatic potential and possibly determining location of metastatic disease, and impacting the outcome of therapy. While the stromal cells are not malignant per se, their role in supporting cancer growth is so vital to the survival of the tumor that they have become an attractive target for chemotherapeutic agents. In this review, we will discuss the various cellular and molecular components of the stromal environment, their effects on cancer cell dynamics, and the rationale and implications of targeting this environment for control of cancer. Additionally, we will emphasize the role of the bone marrow-derived cell in providing cells for the stroma.

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Vitiligo is an autoimmune disease of the skin mediated by CD8 T cells that kill melanocytes and create white spots. Skin lesions in vitiligo frequently return after discontinuing conventional treatments, supporting the hypothesis that autoimmune memory is formed at these locations. We found that lesional T cells in mice and humans with vitiligo display a resident memory (T) phenotype, similar to those that provide rapid, localized protection against reinfection from skin and mucosal-tropic viruses. Interleukin-15 (IL-15)-deficient mice reportedly have impaired T formation, and IL-15 promotes T function ex vivo. We found that both human and mouse T express the CD122 subunit of the IL-15 receptor and that keratinocytes up-regulate CD215, the subunit required to display the cytokine on their surface to promote activation of T cells. Targeting IL-15 signaling with an anti-CD122 antibody reverses disease in mice with established vitiligo. Short-term treatment with anti-CD122 inhibits T production of interferon-γ (IFNγ), and long-term treatment depletes T from skin lesions. Short-term treatment with anti-CD122 can provide durable repigmentation when administered either systemically or locally in the skin. On the basis of these data, we propose that targeting CD122 may be a highly effective and even durable treatment strategy for vitiligo and other tissue-specific autoimmune diseases involving T.

Bacterial pathogens synthesize numerous proteins that are either secreted or localized within bacterial cells. To address the impact of antigen compartmentalization on T cell immunity, we constructed recombinant Listeria monocytogenes that express a model CD8T cell epitope as a secreted or nonsecreted fusion protein. Both forms of the antigen, either secreted into the host cell cytoplasm or retained within bacterial cells, efficiently prime CD8 T cell responses. However, epitope-specific CD8 T cells confer protection only against bacteria secreting the antigen but not against the bacteria expressing the nonsecreted form of the same antigen. This dichotomy as a result of antigen compartmentalization suggests that bacterial antigens are presented by multiple MHC class I pathways to prime CD8 T cells, but only the endogenous pathway provides target antigens for CD8 T cell-mediated protective immunity.

Aging is the single most common risk factor for cancer. Peripheral and marrow-derived stem cells are long lived and are candidate cells for the cancer-initiating cell. Repeated rounds of replication are likely required for accumulation of the necessary genetic mutations. Based on the facts that mesenchymal stem cells (MSC) transform with higher frequency than other cell types, and tumors in aged C57BL/6 mice are frequently fibrosarcomas, we used a genetically tagged bone marrow (BM) transplant model to show that aged mice develop MSC-derived fibrosarcomas. We further show that, with aging, MSCs spontaneously transform in culture and, when placed into our mouse model, recapitulated the naturally occurring fibrosarcomas of the aged mice with gene expression changes and p53 mutation similar to the in vivo model. Spontaneously transformed MSCs contribute directly to the tumor, tumor vasculature, and tumor adipose tissue, recruit additional host BM-derived cells (BMDC) to the area, and fuse with the host BMDC. Unfused transformed MSCs act as the cancer stem cell and are able to form tumors in successive mice, whereas fusion restores a nonmalignant phenotype. These data suggest that MSCs may play a key role in age-related tumors, and fusion with host cells restores a nonmalignant phenotype, thereby providing a mechanism for regulating tumor cell activity. [Cancer Res 2007;67(22):10889-98]